The launch means the Endeavour didn't make the record books for the most number of scrubbed attempts. Those were in 1995 and 1986, when it took seven tries to get off the ground. In 1986, Bill Nelson, who now represents Florida in the Senate, and Charlie Bolden, Barack Obama's nominee to lead NASA, were on board.

This mission, originally scheduled for flight last month, was delayed three times because of bad weather and twice because of hydrogen fuel leaks.

Each delay costs about $1 million for fuel and employee overtime, said NASA spokesman Allard Beutel. But the cost can easily be absorbed by the $3.6 billion budgeted for five shuttle missions in the 2009 fiscal year.

"It just means you can't use that money somewhere down the line," he said.

"Scrubs aren't fun," he wrote at 10 p.m. Sunday, a few hours after the crew climbed out of the shuttle. "I've been in this situation before. You just have to roll with it."

At 3:30 p.m. Wednesday, he wrote: "Hope the next tweet is from orbit."

By 4 p.m., the seven astronauts were strapped into the shuttle and ready to head to the International Space Station while NASA weather experts monitored storms in the area.

But none came close enough to delay the launch.

During the 16-day mission that includes five space walks, astronauts will install a platform outside the space station that's part of Japan's Kibo laboratory. The so-called front porch will allow experiments that require direct exposure to space. The platform can hold 10 experiments at a time. A robotic arm will transfer experiments to and from the platform from inside the shuttle, reducing the need for space walks.

The seven-member team on the Endeavour will join six resident astronauts on the space station. It will be the largest number of people on board the craft at the same time.